Using surveillance systems employing digital recorders for recording obtained data it is important to be reliable when making these recordings. This ensures that recordings will always be present whenever an event occurs that requires the recordings to be replayed.
Digital recorders for surveillance systems are equipped with recording media such as USB memory sticks, CD/DVD/Blue-Ray optical disks and state of the art hard disks. Each of these recording media can store recordings of surveyed audio, video and collected metadata.
Generally, a digital recorder consists of a control unit, and one or more recording apparatus. In state-of-the-art digital recorders the recording apparatus is field replaceable. A main technical feature of the recording apparatus is the capability to guarantee reliability of the recordings made by the digital recorder. It should be noted that most recording apparatus have physical moving parts such as hard disks and optical disk drives having moving heads and spindles, USB memory sticks having embedded NAND flash with limited lifetime. These moving parts limit the physical lifetime of the recording apparatus.
During the lifetime of a digital recorder the recording apparatus and its subsystems will have to be replaced. If the recording apparatus is replaced in the field, the digital recorder supplier has to ensure that the replaced recording apparatus has required quality characteristics.
US 2002/0135684 A1 discloses a method of switching between video signals in an image switching apparatus which has a switch for switching between a video signal supplied by a camera and a video signal supplied by a recording apparatus. Furthermore, a circuit for processing the video signal coming from the recording apparatus is provided. The processing circuit compares the video signal coming from the recording apparatus with the video signal supplied by the camera. Afterwards it sets an operating mode on the basis of the comparison result.